Switching system



Ju1y 15.-' 1924. v

' L- A. MORTIMER SWITCHING SYSTEM Filed Sept. 24. 1920 Mme/War Lay 5 4 Hoff/mar I Hb Patented July 15, 1924.

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LOUIS A. MORTIllIIER, OF NEW YORK, 1l.- Y., ASSIGN-OR TO WESTERN ELECTRIC COMI- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

SWITCHING SYSTEM.

Application filed September 24, 1920. Serial N0. 412,480.

To all whom it may concern:

Be it known that I, LOUIS A. MORTIMER, a citizen of the United States, residing at New York, in the county of New York, State of New York, have invented certain new and useful Improvements in Switching Systems, of which the following is a'full, clear,.

concise, and exact description.

This invention relates to improved methods and means for controlling switching systems, and more particularly to those applicable to transmission lines composited for simultaneous telephony and telegraphy.

For signaling, in such systems, alternating current of two frequencies is generally used. A frequency of approximately 16 cycles per second, which is the frequency of the current commonly used to ring telephone bells, is used for the actuation, of local relays which connect to the line 135 cycle current to signal the distant station. This latter frequency is sufliciently high so as not to cause the improper operation of the telegraph instruments on the line.

It has been found in such systems that certain irregularities of operation are sometimes encountered which it is desirable to avoid. One of these, is the increase in im' pedance of the receiving circuit which results, on an incoming ring, from the opening of the secondary winding of the repeating coil connected in the circuit, and which reduces the efi'ective length of line over which it is possible to obtain satisfactory ringing signals.

Another diiiiculty is the cyclic surging of certain relays in the transmitting and receiving circuits which occurs under certain conditions, which will be subsequently discussed.

It is the object of this invention to overcome these difliculties and maintain the system in satisfactory working condition. 7

To attain this object in accordance with one feature of the invention, a relay is provided which short-circuits the secondary winding of the repeating coil in response to an incoming signal thereby preventing a rise in the impedance of the circuit which would result if the secondary circuit were opened by the actuation of the ringing control relay.

To further attain this object in accordance with another feature of the invention, the cyclic surging of the relays in the transmitting and receiving circuits above mentioned is prevented by making sluggish the ringing control relay of the receiving circuit and by placing it under the common control of the low frequency relay of the transmitting circuit and the high frequency relay of the receiving circuit, details of which are given in the subsequent description.

The nature of this invention will fully appear from the following specification and annexed drawing which shows diagrammatically circuits R and R of Figures 1 and 2 which embody the improvements described above together with other circuits which are not a part of this invention. These latter circuits show only sufficient details to explain the working .of the invention and do not contain all features necessary for regular commercial working.

Fig. 1 shows apparatus at one end of a transmission line L, which consists of a composite ringer circuit R containing the improvements previously mentioned which avoid surging and the increase of impedance of the receiving circuit resulting from an incoming ring. Fig. 2 shows an other form of composite ringer circuit, R at the end of a transmission line L which also embodies the improvements for avoiding the surging difliculty previously mentioned. To explain the operation of these circuits there are also shown in Fig. 1, a toll cord circuit C, a trunk. circuit Tand a subscribers line circuit S. As explained above, the circuits C, T and S are not shown in complete detail, only such features being given as are necessary to explain the opera tion of the invention.

In order to indicate their slow operating characteristics arrows are shown cutting the armatures of relays 1, 4, 6, 25, 32, 33, 35 and 36 and pointing in the directions in which such armatures move slowly.

It is thought that the invention may be more fully comprehended from the following description of the operation of the system shown.

Referring to Fig. 1 of the drawing, assumethat 135 cycle ringing current from a distant office coming in over line L and passing through the normal contacts of slow operating relay 1, windings of repeating coil 2, and relay 3, causes relay 3 to break its normal contact and to open an obvious circuit from battery, through the winding of normally operated, slow releasing relay 4,

. thereby causing its release. The release of the insertion of plug 9 into jack 8, disconnecting drop 7 at the contacts of jack 8. The

operator, by connectingto the cord circuit C a telephone set (circuit not shown) and ascertaining that a connection with subscriberis line. circuit S is required, communicates with an operator in charge of trunk circuit T over a call wire circuit (not shown). The operator in control of trunk circuit T having been informed that a connection with subscribers line S is desired, assigns to this connection trunk circuit T terminating in ack 10 which is in reach of the operator in control of cord circuit C. Plug 11 is then inserted into jack 10 and plug 12, by the trunk operator, into jack 13, on the contacts of which terminates subscribers line S. The

insertion of plug 12 into jack 13 causes the operation of cut ofi relay 20 through a circuit extending from battery, through resistance 21, sleeve contacts of plugs 12 and jack 13 and winding of relay 20 to ground. The

operation of relay 2O disconnects line relay 19.

The operator in control of cord circuit C then actuates ringing key 14, causingthe operation, by 16 cycle ringing current, of

relay 15 over-the following circuit: sourceof 16 cycle current,lower alternate contact of key 14, ring contacts of plug 11 and jack 10, lower right-hand winding of repeating coil 16, winding of relay 15, condenser 17 upper right-hand winding of repeating coil 16, tip contacts of jack 10 and plug 11, and upper alternate contact of key 14 to ground. The actuation of relay 15 causes the operation over an obvious circuit of relay 18, which causes the ringing of the telephone bell of subscribers line S over the following circuit: source of 16 cycle ringing current, lower alternate contact of relay 18, ring contacts of plug 12 and jack 13, subscribers set of subscribers line S, tip contacts of jack 13 and plug 12, upper alternate contact of relay 18 to ground. On removing the receiver from its hook, the subscriber of line S is free to converse over the completed circuit to the distant subscriber at the other end of line L.

l/Vhen relay 5 operated in response to the incoming ringing current from line L, it

short-circuited through its contact over an obvious circuit, the tip and ring conductors of the composite ringer circuit R, preventing the opening of the circuit through the left-hand windings of repeating coil 2 which would be caused'by the actuation of relay 6. As the open circuiting of the windings of repeating coil 2 would cause a considerable increase in the impedance in series with the winding of relay 3, thereby tending to prevent the satisfactory operation of relay 3, this action of relay 5 accomplishes one of the objects of the invention.

Another feature of the invention is made evident by the following description of an outgoing call. Assume that the subscriber of line S desires a telephonic connection with a subscriber located at the distant end of line L, and that a circuit leading to jack 8 and similar to that described above, has been built up, by the operator in control of cord circuit C. The operator actuates ringing key 22 thereby operating relay 23 over the following path: source of 16 cycle current, lower alternate contact of key 22, ring contacts of plug 9 and jack 8, lower normal contact of relay 6, lower left-hand winding of repeating coil 2, winding of relay 23, condenser 24, upper left-hand winding of repeating coil 2, upper normal contact of relay 6, tip contacts of jack 8 and plug 9,'upper alternate contact of key 22 to ground. The actuation of relay 23 causes the operation over obvious circuits, of relay 1 and slow releasing relay 25. The reason for the operation of relay 25 will be given subsequently in connection with the description of another featureof the invention. Relay 1 by its operation, impresses on line L, through its alternate cont-acts, 135 cycle ringing current. It is found, in practice that although relay 3 may be electrically and mechanically tuned to operate only on 135 cycle'current, nevertheless, the 16 cycle current impressed on the tip and ring conductors of circuit R may cause a momentary opening of the normal contact of relay 3. Then relay 23 operated, a second circuit for relay 4 was completed from battery through the winding of relay 4 and the lefthand contact of relay 23 to ground. This alternate circuit, will accordingly preventthe release of relay 4, and the consequent operation over an obvious circuit of relay 6. lVithout this or some similar circuit arrangement, which is a feature of this invention, relay 6 by its operation would interrupt the tip and ring conductors of the circuit R, and cause a discontinuance of 16 cycle ringing current, thereby permitting relay 3 to definitely close its contact and reoperate relay 4, thereby causing the release of relay 6, and the reconnection of 16 cycle current to the tip and ring conductors of circuit R. This would cause relay 3 to again momentarily open its contact and the action just described would be repeated and surging would result. However, as eX- plained above, this difiiculty is avoided by the use of the left hand alternate contact on relay 23 to form a second holding circuit for relay 4.

In connection with the description of an outgoing call given above, slow releasing relay 25 was operated simultaneously with relay 1. The function of this relay will be understood from the following description.

It has been found in practice that even the addition of the left-hand contact of relay 23, may not, under all conditions avoid surging ditficulties above referred to. When the operator in control of cord circuit C releases the ringing key 22, the subsequent release of relay 23 will open the holding circuit for relay 4 through the left-hand contact of relay 23 and through its right hand contact will open the circuit through the windings of relays 1 and 25. When relay 25 has also released, the holding circuit for relay 4 is opened and the only holding circuit for said relay 4 is that through the normal contact of relay 3.

It has been found in practice that when the ringing key 22 has been restored to nrmal that an impulse from the battery connected to the contacts of relay 26 will cause a momentary operation of relay 3 over the following path: from battery, through the left-hand contact of relay 26, lower righthand winding of repeating coil 16, ring con tacts of jack and plug 11, lower normal contacts of keys 14 and 22, ring contacts of plug 9 and jack 8, lower normal contact of relay 6, lower left-hand winding of repeating coil 2, condenser 27, upper left-hand winding of repeating coil 2, upper normal contact of relay 6, tip contacts of jack 8 and plug 9, upper normal contacts of keys 22 and 14, tip contacts of plug 11 and jack 10, upper right-hand winding of repeating coil 16 and right-hand contact of relay 26 to ground. The impulse of current through the left-hand windings of repeating coil 2 induces current in a secondary circuit which includes the upper and lower right-hand windings of repeating coil 2 in series with the winding of relay 3. This impulse of current will cause the momentary opening of the contact of relay 3 and the consequent release of relay 4.

Assuming that the other two holding circuits through the left-hand contact of relay 23 and contact of relay as explained above are already open and that relay 4 has released, relay 6 will operate through an obvious circuit closed by the contact of relay 4. The battery connection fromthe contacts of relay 26 will then be interrupted at the normal contacts of relay 6. Since, however, the breaking of the contact of relay 3 i only momentary, the consequent release of relay 4, and the operation of relay6, will alsobe but momentary. Consequently relay 6 will immediately release and reconnect battery to the circuit traced above which will again cause the-momentary operation of relay 3 and a repetition of. the action just described, which will tend to continue automatically. r

This surging action may also be initiated, under certain line and voltage conditions, 75 by the opening of the circuit through the winding of relay atthe telephone switchhook of subscribers line S. This will cause the release of relay 40 through a circuit which may be traced as follows: from battery through the winding of relay 40, lower left hand winding of repeating coil 16, lower normal contact of relay 18, ring contacts of plug 12 and jack 13, switchhook contacts of subscribers line S, tip contacts of jack 13 and plug 12, upper normal contact of'relay 1S and upper left-hand winding of repeating coil 16 to ground. The release of relay 40 causes the release of relay 26, and connects battery, at the lefthand contact of relay 26, in series with the right-hand windings of repeating coil 16, so as to momentarily operate relay 3, over the circuit previously traced in connection with the actuation of ringing key 22. This operation of relay 3 may sometimes be sufficiently prolonged to permit the release of slow releasing relay 4 and the subsequent; operation of relay 6, thereby impressing 16 cycle ringing current on the tip and ring 100 conductors of circuits T and C. This may charge the condensers 17, 41, and 42 and on the subsequent release of relay 6, the condensers may discharge so as to operate momentarily relay 23 and again relay 3. Surg- 105 ing however, is prevented inv this case, as well as in those previously mentioned, in accordance with another feature of this inven tion, by making the relay 25 slow releasing. The holding path of relay 4 is then main- 110 tained through the contact of relay 25 until the momentary disoharge'through the winding of relay 3 is completed; after which there can, of course, be no surging as described above Fig. 2 shows another form of composite ringer circuit, R which is also arranged to prevent surging. Its operation is similar to that described for circuit B, Fig. 1. When plug 9 is inserted into ack 28, the drop 29 is 120 disconnected at the tip and ring contacts of jack 28. \Vhen key 22 is actuated, 16 cycle ringing current actuates relay 30 over the following circuit: source of 16 cycle current, lower alternate contact of key 22, ring con- 126 tacts of plug 9 and jack 28, lower normal contact of relay 36, winding of relay 30, condenser 31, lefthand winding of retardation coil 39, upper normal contact of relay 36, tip contacts of jack 28 and plug 9 and upper ll) alternatecontact of key 22 to ground. The actuation of relay 30 causes the operation of slow operating relay'32 and slow releasing relay 33. Relay 32 by its operation connects 135 cycle current to the conductors of line L On an incoming ring, relay 34 is operated by 135 cycle current through the upper normal contact of relay 32, the righthand winding of retardation coil 39, condenser 37, the winding of relay 34, and the lower normal contact of relay 32. ,The open iug of the normal contact of relay 34 causes the release of normally operated slow releasing relay 35 and the operation over an obvious circuit of relay 36 which .actuates the drop 29 with 16 cycle ringing current through the alternate contacts of said relay 36, and the normal contacts of jack 28.

.I-Iolding circuits for relay 35 are established through the lefthand contact of relay 30 and the contact of relay 33. These holding circuits prevent surging in the same manner as the holding circuits for relay. 4, through the left-hand contact of relay 23 and the contact of relay 25, prevented surging in the case of circuit R.

Circuit R of Fig. 2 has also the desirable feature of being arranged to avoid interference from stray telegraphic currents. To accomplish this the circuit including the winding of relay 30, condenser 31 and the left-hand winding of retardation coil 39 is made resonant to 16 cycle current or to current of any other frequency that may be used for an outgoing ring. Thecircuit including the winding of relay 34, condensers 37 and 38 and the right-hand winding of retardation coil 39 is made resonant to 135 cycle current or to current of any other frequency which may be desirable to use for an incoming ring. Since the circuits including the right and left hand windings of retardation coil 39 are each made resonant to the frequency of the current which operates the relays in the respective circuits, stray current impulsesfrom the telegraphic operation of the line are in general excluded, and the effect of interference much reduced.

It will be evident to one skilled in the art that numerous variations in the specific circuit arrangements described, may be made Without departing materially from the general plan and scope of this invention, and with this in view it is desired to define the invention more broadly in accordance with the appended claims.

What is claimed is: a

1.- In a switching system, a telephone line, a source of signaling current at one end of said line, a transmitting circuit responsive to said signaling current, a second source otcurrent, a third source of current to signal over the line from the distant end thereof, a receiving circuit responsive to said third source of current and means to prevent an oscillatory surging of said transmitting and receiving circuits initiated by the response of the receiving circuit to said second source of current.

2. In a switching system, a telephone line, a link circuit associated with said line, a source of signaling current at one end of the line, a transmitting circuit responsive to said signaling current, a second source or" current, ,a third source of current to signal over the line from the distant end thereof, a relay responsive to said third source of current, a relay controlling the connection to said link circuit of said first mentioned source of signaling current, said second mentioned relay being under the control of said first mentioned relay, and means for delaying the action of said second relay in re sponse to the momentary action of the first relay initiated by said second source of current, to prevent surging oscillation of said relays.

3. In a switching system, a transmission line having inner and outer sections, a repeating coil inductively uniting said sections and having its primary winding connected to the outer section, a signal associated with the inner section, a source of current associated with the inner section, a relay to apply current from said source to said signal to cause the operation of said signal, and means responsive to ringing current received over the outer section of said line for energizing said relay and for short-circuiting the secondary circuit of said repeating coil.

4. In a switching system, a transmission line having inner and outer sections, signal current responsive and signal current applying means associated with each section, a slow to release relay controlling the operation of the signal current applying means for the inner section, a second slow to release relay controlled by the signal current responsive means associated with the inner section, and circuit connections whereby said first slow tOl release relay is jointly controlled by the signal current responsive means connected to the inner and outer sections and by! said second slow to release relay.

5. In a signaling system, a normally closed circuit, a source of current associated therewith, a slow to release relay actuated in response to the application of current from said source to said circuit, and switching means controlled by said slow to release relay for connecting a bridge across said circuit and thereafter opening said circuit on one side of said bridge.

6. In a signaling system, a source of current, a circuit including means responsive to current from said source, a second source of current, a second circuit including means responsive to said second source, a third source of current and means to prevent oscillatory surging of said circuits due to the response of said second mentioned means to current from said third source.

7. In a signaling system, a source of current, a circuit including means responsive to current from said source, a second source of current, a second circuit inductively related to said first circuit and including means responsive to current from said second source and means to prevent an oscillatory surging of said circuits due to a momentary response of the means in said first mentioned circuit.

8. In a signaling system, a line circuit having inner and outer sections, a source of current for each section, a signaling source associated with the inner section and relays responsive to current from the source associated with the outer section one for opening the conductors of the inner section to connect the source for that section thereto and to short circuit said conductors to prevent a change in impedance in the line circuit, the opening of the conductors being effected subsequently to the short circuiting thereof.

9. In a signaling system, a line circuit comprising a plurality of inductively coupled sections, sources of current of different frequencies associated with said sections, means responsive to current of one of said frequencies associated with one of said sections to connect another of said sources of current to another of said Seetionsand means for bridging said latter mentioned section prior to the connection of said current source thereto, said means being responsive to current from the source associated with the first mentioned section.

10. In a signaling system a chain of relays having their input and output circuits respectively interconnected, one of"said relays being selectively responsive to current of one frequency, and another of said relays being responsive to currents of another frequency, a source of current to cause surging of said relays and a circuit controlling device to prevent surging of said relays.

11. In a signaling system a plurality of relays selectively responsive to currents of different frequencies, means to interconnect the input and output circuits of said relays whereby surging is adapted to occur and a retarding device to prevent surging.

1:2. In a signaling system, a repeating coil, relays associated with the windings thereof and selectively responsive to currents of different frequencies, circuit opening and closing means associated with each of said windings and each controlled by a relay associated with another winding and additional circuit closing means associated with one winding and controlled by a relay associated with another winding.

13. In a signaling system, a repeating coil, relays associated with the windings thereof and selectively responsive to, currents of different frequencies, switching means associated with each of said windings and controlled by said relays associated with other of said windings and a slow to release relay controlled by one of said relays to prevent surging.

In witness whereof, I hereunto subscribe my name this 21st day of September A. D., 1920.

LOUIS A. MORTIMER. 

